Since their origin 479 million years ago, insects have been a crucial part of terrestrial ecosystems. At least 900 thousand living species are known, making up around 80% of the world’s total species; it is estimated that there are 10 quintillion individual insects alive at any given time (that’s 10,000,000,000,000,000,000!). We have been hearing concerns over bees going extinct for years, but now it seems that the situation is much more dire, and affects insects across the board. A global review has revealed that more than 40% of insect species are declining, and a third are endangered, meaning mass extinction is likely in most regions over the next few decades. 80% of insect biomass has disappeared in the last 25-30 years. Do we know what is causing this crisis? And what can we do to help save our insect populations?
Insects are important to their ecosystems, as well as humans, for many reasons. Firstly, they are essential for pollination- 80% of flowering plants rely on insects for this. Without pollination, plant populations will decline, leading to a trophic cascade as animals run out of food. Insects are also at the heart of every food web, providing nutrition for many different kinds of animals at higher levels. Without them, animals begin to starve and look for other sources of food. These effects have already been observed in the Puerto Rican rainforest, where 98% of ground insects have disappeared, resulting in a 50-65% decline in the frogs and birds who fed on them. Also, much of the nutrient cycling, conditioning and aeration of soil is performed by reducers and recyclers such as beetles, flies and cockroaches, alongside their arthropod relatives.
Obviously, humans also depend on these natural ecosystems for things like food, water, oxygen and materials, and therefore rely on insects for these reasons also. They are needed at various stages of food agriculture; bees and other pollinators are vital in pollinating most of the world’s food crops, as well as being used as biological pest control. Their loss would mean food shortages- especially worrying with an ever growing population that requires an ever growing amount of food. We also rely on some species for commercial products, such as silk (from silk worms), dye (from
cochineal or kermes), cotton (pollinated by bees), and beeswax.
So what is causing this global decline in insects?
A new study has has for the first time reviewed 73 separate investigations into insect declines from around the globe, conducted over the past 13 years, and examined the underlying causes. The main drivers of decline have been identified as, in order of importance: the destruction of habitats and conversion to intense agriculture and urbanisation, pollution due to synthetic fertiliser and pesticide use, biological factors like invasive species and disease, and climate change.
The intensification and expansion of agriculture and urbanisation is destroying natural habitats and fragmenting landscapes. Fragmentation isolates populations and decreases population size, meaning the amount of inbreeding increases and the risk of extinction grows due to a lack of genetic variation- individuals cannot be recruited from adjacent areas to widen the gene pool, and so all are vulnerable to change in the same way. Fragmentation also means that insects are trapped in habitats which could potentially become uninhabitable.
The expansion of agriculture also means an increase in the use of fertilisers and synthetic pesticides. By far the most damaging are the insecticides used to control crop pests, followed by fungicides; herbicides do not affect insects directly but act to reduce the biodiversity of the plants on which insects feed. Alongside these, other pollutants such as sewage and landfill leachate are having a detrimental effect on insects. The biodiversity of plants and insects negatively correlates to the amount of nitrogen entering terrestrial systems, explaining the huge losses observed since the introduction of synthetic fertilisers in the early 20th century. Industrial chemicals are likely to have a huge impact on the health of insect communities, although this has not been adequately studied. Aquatic insect species have also taken a hit, due to the acidification of waters caused by industry and climate change. The effects of these issues can be observed in the invasion of pollution-tolerant species into the affected areas, replacing the biodiversity losses. It can be seen that the combination of all these pollutants would be a lot for the insect world to deal with!
Biological factors like parasites and pathogens have been shown to contribute greatly to the decline of many insect species, most notably the honey bee. Exotic species can out-compete native species once introduced, or cause their decline through predation or parasitism. In this modern world, as transport networks continue to expand and allow large volumes of passengers to travel faster than ever, the risk of diseases spreading and species being relocated is increased.
Finally, climate change, most notably warming temperatures, is altering the areas and time frame in which insects can live. For example, some species of dragonflies, stoneflies, and bumblebees adapted to colder environments and higher latitudes have had their geographic range reduced.
All of these factors mentioned produce compounding effects when each one reduces insect biodiversity and therefore makes them more vulnerable to the impacts of the others. If we are not careful, we could be looking at a catastrophic collapse of ecosystems, from the bottom up.
That being said, what can we do to help protect our insects from population collapse?
On an individual level, we can promote insect biodiversity in our gardens and local areas, for example by building a bug hotel, or simply letting grass grow longer and planting wildflowers- insects like mess!
The most obvious way to solve many environmental problems, not just those associated with insect extinction, is to reduce the effects of climate change. Decreasing the amount of pesticide used could be possible by using natural alternatives like ‘companion planting’ or by using more natural predators like ladybirds and beetles.
The solutions that will definitely make a difference need to be carried out by the agricultural industry and companies on a global scale, which is often not economically viable. However, businesses and governments need to start making sacrifices now to protect the world of the future- sustainability should be our main priority.